The present invention relates to nonwoven fabrics and to processes for producing the nonwoven fabrics. More specifically, the invention relates to nonwoven fabrics suitable for use in absorbent products, such as disposable diapers, adult incontinence pads and sanitary napkins, and the like.
Nonwoven fabrics a re desirable for use in a variety of products, including bandaging materials, garments, diapers, supportive clothing and personal hygiene products. Nonwoven fabrics that are capable of transmitting body fluids to an absorbent layer while maintaining skin dryness are particularly desirable for use as a coverstock layer in disposable personal care products.
Disposable absorbent products, such as disposable diapers, sanitary napkins, and the like, typically include a liquid impermeable outer covering, an absorbent layer, and an inner layer which contacts the skin of the wearer. To provide a comfortable yet effective product, the inner layer ideally permits liquid to flow through it rapidly into the absorbent layer (xe2x80x9crapid strike throughxe2x80x9d) but does not permit or, at a minimum does not facilitate, re-transmission of liquid from the absorbent layer to the xe2x80x9cwearerxe2x80x9d side of said inner layer (xe2x80x9cresists rewetxe2x80x9d). Such inner layers are referred to in the art as coverstock, topsheet, or, in diaper applications, diaper liner.
In addition to liquid transport properties described above, the coverstock must have sufficient strength to allow for converting it, i.e., incorporating it into the final product, and for resistance to failure during vigorous movements by the user. On the other hand, while strength is essential, the coverstock should also present a soft comfortable feel against the user""s skin. Currently these conflicting requirements, both softness coupled with strength and rapid strike-through coupled with low surface rewet, are met only imperfectly, typically with the use of coverstock stock made from thin, low basis weight (about 22 grams per square meter or about 20 grams per square yard) carded or spunbonded nonwoven fabrics.
Others have attempted to provide products having improved coverstock performance. U.S. Pat. No. 4,041,951 to Sanford discloses a topsheet containing a multiplicity of depressed areas which intimately contact the uppermost surface of a substantially planar, moisture absorbent layer, while the non-depressed areas of the topsheet contact the skin of the wearer in use. The depressed areas are formed by embossing a nonwoven web between a patterned steel roll having male projections thereon and a rubber coated roll. A pattern is formed on the nonwoven web such that the caliper or the density of the web at the depressed embossed sites is not changed from that seen in the un-embossed part of the roll.
U.S. Pat. No. 4,854,984 to Ball et. al. teaches a method for dynamically bonding a plurality of laminae together wherein the laminae are forwarded in face to face relation through a pressure-biased nip between a patterned nip and opposing nip, each independently driven to maintain a predetermined surface velocity differential between them. The differential velocity is stated to contribute to shear energy to enable dynamic, mechanically induced bonding.
Suzuki et. al. in U.S. Pat. No. 4,704,112 describe a diaper topsheet made by combining two layers of nonwoven webs at their interface by fiber fusion or by hydroentangling. At least one of the webs must be apertured.
Meyer et.al. in U.S. Pat. No. 4,798,603 teach an absorbent article, i.e., a diaper, that includes a second nonwoven layer under the topsheet and above the absorbent core composed of a material less hydrophilic than said absorbent core and having an average pore size smaller than the topsheet layer pore size. The patent states that bonds used to attach the transport layer to the rest of the diaper construction should not extend completely through the transport layer thickness.
Datta et. al. in U.S. Pat. No. 4,892,534 describe a nonwoven liner fabric particularly useful for feminine care applications that contains at least three layers of thermoplastic filaments which are laid down via spunbond methods and then bonded together.
Schmalz U.S. Pat. No. 5,045,387 is directed to a topical treatment of polyolefin containing nonwoven webs. The patent describes the use of a facing or cover sheet for sanitary products such as diapers wherein the webs are made from polypropylene and can be formed by spunbonding. The patent further states that the nonwovens can be formed of one or more bonded webs, and that the nonwoven fabric can be embossed and/or calendar printed with various designs and colors.
U.S. Pat. Nos. 4,077,410; 4,332,253 and 4,762,520, 4,883,707; 4,304,234 all disclose the use of plural layers of nonwoven fabrics as the topsheet in a sanitary product. Braun in U.S. Pat. No. 4,668,566; Raley in U.S. Pat. No. 4,761,322; and Modrak in European Patent Application 0490476-A1 teach the combination of one bonded nonwoven web with an unbonded nonwoven web. The resulting combination is bonded together so a final structure results. Meitener in U.S. Pat. No. 4,493,868 teaches methods to put multiple bond patterns on a nonwoven web.
U. S. Patent No. 3,934,588 to Mesek et al. discloses a diaper topsheet with areas of preferential flow, surrounded by borders having less transmissivity for aqueous liquids than the preferential flow areas. Mesek teaches the use of areas of reduced thickness via a lesser amount of fibers, areas of increased surfactant concentration, or areas of increased hydrophobic binder application to produce his areas of preferential flow or resistance to flow.
U.S. Pat. No. 4,863,785 to Berman et. al. teaches the combination of a meltblown fabric layer between two prebonded spunbonded nonwoven layers, all continuously bonded together, to form a composite that is highly resistant to the penetration of liquids and thus useful as a sterilization wrap for medical applications. U.S. Pat. No. 4,041,203 to Brock et al. teaches the combination of a meltblown fabric layer between two spunbonded layers, all bonded together by discrete bond regions, to form a composite that is also useful in medical applications which require a barrier layer to prevent the passage of liquid and bacteria.
The present invention provides a multilayer thermally bonded nonwoven fabric which is particularly useful as a component in an absorbent article. The nonwoven fabrics of the present invention provide improved surface visual patterns or designs. Hydrophilic nonwoven fabrics of the present invention can provide superior liquid transport properties and thus are particularly useful as the liner layer in an absorbent article. These desirable properties are achieved at reasonable cost while preserving acceptable softness and strength properties.
The nonwoven fabrics of the invention include at least two prebonded nonwoven webs. The term xe2x80x9cprebondedxe2x80x9d refers to the use of nonwoven webs that are each individually bonded to form coherent webs. That is, each of the prebonded webs includes a multiplicity of intralaminar bonds between fibers that bond the fibers of the prebonded nonwoven webs together. Preferably, the prebonded webs are bonded by discrete point bonds located at spaced locations throughout each of the webs.
The multilayer thermally bonded nonwoven fabric also includes a plurality of interlaminar thermal bonds which secure the prebonded webs together. To form the interlaminar thermal bonds, discrete areas of the fibers of the prebonded webs are thermally treated so that the fibers are compressed and fused together. In a preferred embodiment of the invention, the discrete areas of compressed and fused fibers form continuous line bonds, which in turn form a pattern of intersecting continuous lines. Further, using such a bond pattern, a quilted, or pillowy texture can be imparted to the surface of the fabrics of the invention.
In another embodiment of the invention, disposable absorbent articles are provided which include as a component a multilayer thermally bonded fabric according to the invention. Certain hydrophilic fabrics of the invention are particularly useful as a component, such as a liner or topsheet layer, in disposable absorbent products such as diapers and the like. In this embodiment of the invention, an absorbent body or layer is sandwiched between the fabric of the invention and an outer backsheet layer of a substantially liquid impermeable layer.
Hydrophilic nonwoven fabrics of the present invention can provide superior liquid transport properties, i.e., permit liquid to flow through the fabric rapidly while retarding re-transmission of the liquid to the surface of the fabrics. Further, the fabrics of the invention provide a soft, comfortable feel while also having good strength properties.